In the production of hollow plastic containers it is common to injection mold a preform and then blow mold the preform to achieve the final shape of a container. Typically, at least a body portion of the container is of multilayer construction in which one or more intermediate layers form a barrier against gas transmission through the container. Such multilayer blow molded containers are often used for medical-type products such as pharmaceuticals. Unfortunately, however, pharmaceuticals are sometimes counterfeited and packaged in counterfeit containers that look identical to genuine containers used to market genuine pharmaceuticals. Accordingly, such counterfeit containers are used to deceive pharmacists and consumers into buying counterfeit pharmaceuticals.
In accordance with one aspect of the present invention, a multilayer molded plastic container has a sidewall with at least one and preferably two layers of matrix resin, and at least one intermediate resin layer. In the preferred embodiments of the invention, the intermediate layer(s) are of barrier resin polymer to retard migration of gases, water vapor or flavorants through the container sidewall. However, as will be described, the intermediate layer resin can be of any suitable type, including the same resin as the matrix resin layer(s). In accordance with this first aspect of the invention, an additive is placed in the intermediate resin layer(s) to render the intermediate resin layer(s) visible, either directly or under ultraviolet light. The container sidewall is provided with at least one region or area in which the thickness of the intermediate layer(s) is greater than in other areas of the sidewall. This preferably is accomplished by providing one or more bulges or thickened areas in the sidewall, in which a major portion of the increased sidewall thickness is due to an increased thickness of the intermediate layer(s). In these thickened areas, the apparent density of the additive in the intermediate layer(s) is greater as viewed from outside the sidewall, so that the thickened areas form a visible watermark-like appearance in the sidewall. In the preferred embodiments of the invention, the additive is a fluorescent material that becomes visible under ultraviolet light, or pieces of reflective material such as mica flakes that become visible by reflecting visible light.
In accordance with another aspect of the invention, a method of making a plastic container includes molding a preform having a multilayer construction in at least a portion of the preform sidewall, and then blow molding the body of the preform to form the container. The preform is molded to have at least one radially outwardly extending bulge in its sidewall, in which intermediate sidewall layer(s) account for a major portion of the increased thickness. When the preform body is blow molded, the bulge extends radially inwardly from the container wall. An additive in the intermediate layer in the bulge in the container sidewall becomes visible as watermark-like indicia under ultraviolet or visible radiation, providing identifying information associated with the container.
The multilayer container and preform preferably have N matrix layers (e.g., two or three) and N−1 intermediate layers (e.g., one or two). The matrix layers may be of any suitable resin, such as polyethylene terephthalate (PET) or polycarbonate. The intermediate layer(s) preferably are of barrier resin construction, such as ethylene vinyl alcohol (EVOH) or nylon. However, as recited above, the intermediate layer could also be of PET or polycarbonate in accordance with the broadest aspects of the invention inasmuch as it is the additive in the intermediate layer(s) that provides the distinguishing feature of the invention.